"We know where our daughter is … she's safe," Charles Cox, his wife sitting beside him, said on Tuesday's Today show. "And we know the boys are now back with their mother."

The Coxes also described their last day with the boys, who were in their care and having a good time playing with their cousins until their father, Josh Powell, came to get them. The boys didn't want to go, said their grandparents, but by order of the court it was mandatory that they did.

"I was concerned about the visitation," said their grandfather. "We knew what he was capable of."

Days earlier, a family court judge told Powell that at no time soon was he likely to receive custody of his sons, who were in the care of their maternal grandparents, and that he needed to undergo a psychological review.

"He was feeling cornered," Judy Cox said on Today. "He didn't like us."

'Only Daddy Came Back'

The Coxes also recounted the boys' tale of being on a camping trip in the desert with their parents, who drove off together, but "only Daddy came back," said Judy Cox.

New information is also emerging about Sunday's tragedy, including the fact that 10 gallons of gasoline were in the house, and that Josh had been giving away the boys' toys and sending apologetic email messages to relatives and to his pastor. He said he couldn't live without his boys, according to reports.

In addition, following preliminary autopsies, the Pierce County medical examiner's office said that while Josh, Charlie and Braden died of carbon monoxide poisoning related to smoke from the fire, the younger boy, 5-year-old Braden, also suffered a "chop injury" to the head and neck, and that his older brother, 7, had a similar injury to the neck.

Pierce County Sheriff's Det. Ed Troyer said at a press conference in Graham, Wash., that during the investigation of the house following the explosion, "We recovered a hatchet – a small ax. "It was right there" with the bodies.

"We believe he planned this event out and had taken certain steps. This is definitely a deliberate, planned out event," said Troyer.